1. Field of the Invention
This invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
A fuel injection valve for internal combustion engines of the kind with which this invention is concerned is known for instance from German Patent Disclosure DE 43 03 813 A1. A fuel injection valve of this kind has a valve body, in which a bore is embodied on whose end toward the combustion chamber a valve seat face and at least one injection opening are embodied. A pistonlike nozzle needle is disposed longitudinally displaceably in the bore and is guided sealingly in the bore in a portion remote from the combustion chamber. The nozzle needle tapers toward the combustion chamber, forming a pressure shoulder, and on its end toward the combustion chamber it changes over into a valve sealing face that cooperates with the valve seat face and thus by means of the longitudinal motion of the nozzle needle opens and closes the at least one injection opening. At the level of the pressure shoulder, a radial enlargement of the bore forms a pressure chamber, which continues, surrounding the nozzle needle, in the form of an annular conduit as far as the valve seat face. On its end remote from the combustion chamber, the nozzle needle is acted upon by a closing force exerted in the direction of the valve seat. At the same time, a hydraulic force acts on the nozzle needle counter to this closing force, which because of the fuel pressure in the pressure chamber and the attendant hydraulic force is exerted on the pressure shoulder.
In the substantially conical valve seat face, generally a plurality of injection openings are distributed uniformly over the circumference of the valve body. For uniform injection through all of these injection openings, it is important that in the opening motion of the nozzle needle, the nozzle needle and thus also the substantially conical valve sealing face remain precisely central relative to the bore and thus to the valve sealing face, so that a uniform flow of fuel out of the pressure chamber to the injection openings can be accomplished. Since the nozzle needle is now guided in the bore on the portion remote from the combustion chamber, once the valve sealing face lifts from the valve seat face, there is a very long free length of the nozzle needle between the guided portion and the valve seat face, so that it can easily happen that the nozzle needle will become tilted in the bore, resulting in an uneven inflow of fuel to the injection openings. Precisely at the beginning of the opening stroke motion when there is only a very small gap between the valve sealing face and the valve seat face, such tilting has a major influence on the injection pattern and hence on the quality of combustion.